Liquid immersion freezing systems such as shown and described in U.S. Pat. No. 4,955,209 have been used to quick freeze various types of food and non-food products by direct immersion of a foodstuff or other particulate product into a bath of a cryogenic liquid, e.g. liquid nitrogen, to effect quick freezing of the foodstuff or particulate product. In addition to being exposed to contact with the cryogenic liquid, the particles are also contacted with vaporized cryogenic liquid above the bath.
One of the drawbacks with the prior art immersion-type freezers is that particles of small size and/or low density tend to float in the bath of liquid cryogen as they proceed from one end to the other of the freezing apparatus. Thus, the portion of the foodstuff or particle in direct contact with the liquid may be quick frozen, but the other part of the particle that is not in direct contact with the liquid may not achieve the desired temperature or desired degree of freezing.
Immersion-type freezers are proposed to be used in combination with conventional-type mechanical (non-cryogenic) freezers to provide an initial quick freeze, through freezing being accomplished in a separate freezer that is used in tandem with the immersion-type freezer.